This invention relates to a solvent composition useful for liquid delivery of metal precursors in chemical vapor deposition (CVD) or atomic layer deposition (ALD).
Chemical vapor deposition methods are often used in semiconductor industry to deposit thin films of various materials on a selected substrate. In a traditional chemical vapor deposition (CVD) the vapor of one or more volatile precursors is contacted in chemical vapor deposition reactor with a solid substrate, which has been pre-heated to the temperature above thermal decomposition of at least one of the precursors. For deposition of highly conformal films on complex surfaces, such as deep trenches and other stepped structures, cyclic chemical vapor deposition methods are often used. For example, in an atomic layer deposition (ALD) method, a pulse of one precursor is separated from a pulse of second precursor by a pulse of inert gas. In this case, separate dosing of volatile precursors prevents gas-phase reactions between highly reactive precursors and promotes highly selective surface reactions. ALD is now considered as one deposition method with the greatest potential for producing very thin, conformal films of high K dielectric metal oxides.
While a number of vapor deposition techniquies are described in the literature for deposition of many materials including silicon, silicon dioxide, aluminum oxide, titanium nitride, consistent delivery of precursor vapors to the deposition reactor is still quite challenging for deposition of films containing: titanium, zirconium, strontium, barium, lanthanides and a number of other transition metals. This is mainly due to lack of thermally stable liquid precursors, with relatively high vapor pressure for vapor phase delivery. In many cases, the precursors are solids, whose sublimation temperature is very close to the precursor's decomposition temperature.
A number of precursor delivery systems have been designed to address these challenges. One method, which is already widely used in semiconductor industry for delivery of metal organic precursors, is based on conventional bubbler technology, where inert gas is bubbled through a neat liquid or a molten precursor at elevated temperature. However, this method has several disadvantages. First of all, precise temperature control of the bubbler is required during the single run and between different runs to maintain constant delivery rate of the precursor. A number of precursors have very low vapor pressure at moderate temperatures and have to be heated to 100-200° C. to deliver enough precursor vapors to the deposition reactor by the bubbling method. However, extended periods of time at these temperatures may cause thermal decomposition of the precursors. The precursors may also react with traces of moisture and oxygen introduced to the bubbler during multiple deposition cycles. The examples of precursors with limited thermal stability and/or high reactivity toward moisture include metal alkylamides, metal alkoxides, metal cyclopentadienyls, metal ketoiminates and others. Products of thermal decomposition may plug delivery lines and affect the delivery rate of precursors. Solid precursors delivered from their molten phase may also plug the lines during multiple cooling/heating cycles.
An alternative delivery technique, direct liquid injection (DLI), has several advantages for precursor delivery, including the ability to deliver higher flux of precursor vapors to the chamber, stable operation over reasonable lifetimes, gentle thermal transfer to precursors, and ease of integration with existing commercial deposition chambers. In this method, a liquid precursor or a solution of a precursor and solvent is delivered to a heated vaporization system, whereby the liquid composition is transferred from the liquid phase to the gas phase. Advanced liquid metering of the precursor to the vaporizer provides accurate, stable control of precursor delivery rate. It is critical during the vaporization process that the precursor structure is maintained and decomposition is eliminated. Historically, neat liquid precursors were delivered through DLI. With a suitable solvent, implementation of DLI allows delivery of a wide variety of metalorganic precursors, including solids and highly viscous liquids, which may not be suitable for vapor delivery by the bubbling method.
A number of solvents have been proposed for DLI of metalorganic precursors in prior art, for example: alkanes, glymes and polyamines, for delivery of metal organic precursors.
The prior art generally discloses solvents that can be used in combination with metalorganic precursors, but they do not call out specific benefit regarding the solubility requirements and the thermal requirements.
However, there is still a continued need for developing improved compositions for DLI of highly viscous or solid metalorganic precursors with low vapor pressure.
Prior art in the general field of the Present Invention includes the following references.
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